Ball is Softball

Stadium Unlocks

Hit a Home Run at the following parks to Unlock Each Stadium
Hit A Home Run At: To Get This Stadium
Right Field (San Francisco) Atlantis
Fenway (Boston) Coliseum
Yankee Stadium (New York) Empire
Pet Co (San Diego Padres) Forbidden
Wrigley Field (Chicago) Midway
Citizen's Bank (Philadelphia) Monument
Minute Made Park (Houston) Rocket Park

Tiny Heads

Big Heads

Go to the versus screen and press Right, Square, Square
OR
Square, Square, Right

PS2 | Submitted by GamesRadar

More Time After Each Play

Go to the versus screen and press Left, Square, Triangle, Triangle, Circle, Circle, Circle
OR
Square, Triangle, Triangle, Circle, Circle, Circle, Left .
More time to beat up other players after each play.

MLB Slugfest: Loaded Unlockables

Unlock Lions Team

At Comercia park hit a home run with the Tigers to unlock the Lions Team

PS2 | Submitted by GamesRadar

Unlock Bobblehead Team

Hit ten home runs during a game to get the Bobblehead Team

PS2 | Submitted by GamesRadar

Stadium Unlocks

Hit a Home Run at the following parks to Unlock Each Stadium
Hit A Home Run At: To Get This Stadium
Right Field (San Francisco) Atlantis
Fenway (Boston) Coliseum
Yankee Stadium (New York) Empire
Pet Co (San Diego Padres) Forbidden
Wrigley Field (Chicago) Midway
Citizen's Bank (Philadelphia) Monument
Minute Made Park (Houston) Rocket Park

PS2 | Submitted by GamesRadar

Unlock Sub Zero Team

At Midway park hit a home run to unlock the Sub Zero Team

PS2 | Submitted by GamesRadar

Unlock Scorpion Team

At Midway park hit a home run with Sub Zero to unlock the Sub Zero Team